I would recommend Real-Time Object Oriented Modeling (1994) by Bran Selic, Garth Gullekson and Pault T. Ward, ISBN 0-471-59917-4. It was one of the firsts books I read in this area, and I think that it is one of the classic books on model based software development. Even if it came out already in 1994, I still think that it has a lot of good stuff, especially if you are into the development of real-time systems.